The present invention relates to a picture signal readout system in the facsimile equipment and so on
Furthermore, it relates to a readout system which can read picture data while a manuscript is being shifted.
FIG. 1 outlines an example of an existing facsimile transmitter. In FIG. 1, picture data of a manuscript 1 which is irradiated by the lighting source 4 having the power supply 3 and fed by the roller 2 is read for a line by the CCD (Charge Coupled Device) image sensor (photo-electric conversion element) 6 via the lens 5, amplified by the amplifier 7 after photo-electric conversion and then input to the discriminator 8 as the analog picture signal AP. The discriminator circuit 8 compares the received analog picture signal AP with the discrimination level signal TH which discriminates black and white level, and outputs the digital picture signal DP of logic "1" considering the analog picture signal AP higher than said discrimination level signal TH as the white signal W and the digital picture signal DP of logic "0" considering the analog picture signal AP lower than the discrimination level signal TH as the black signal B. The digital picture signal DP output from the discrimination circuit 8 is input to the picture signal processor 9 and then transmitted to the transmission path via the modulator.
Such facsimile equipment is provided with following means in order to omit transmission of the picture data of the blank portion in view of improving the transmission rate of manuscripts.
Namely, the picture data as many as one line is read by the image sensor 6 indicated in FIG. 1, and this one line length is divided into predetermined number of blocks and it is discriminated whether the black signal B exists or not in each block divided. The block not including the black signal B is not transmitted as the picture signal and only the block including the black signal B is transmitted as the picture signal.
Such existing facsimile equipment has an advantage that the picture signal of the blank portion is not transmitted and the transmission time can be curtailed as much and thereby the send time can also be shortened.
However, above means brings about following disadvantages.
Namely, the image sensor 6 indicated in FIG. 1 cannot read picture data momentarily but, reads within a predetermined period, and the time for starting read of picture data is specified by the time for sending the preceding line data to the transmission path. When the preceding line data is transmitted, it is immediately required to transfer the data read by the image sensor 6 but, the read time of the image sensor 6 is constant and may be longer than the transmission time of the preceeding line.
On the occasion of reading picture data by the image sensor 6, the paper is fed as much as the width of one scanning line from the preceding line by the roller 2 and when the manuscript stops, data is read. However, if the time for sending data of preceding line is short as explained above, this situation may sometimes require extra time for the image sensor 6 to start read of picture data from the interim time during paper feed. Particularly, when the preceding line is all white, the time required for sending the data of preceding line to the transmission path becomes the shortest and situation may some time make it impossible for the image sensor 6 to read accurately the picture data of the next line of the manuscript having been fed.
Such process is explained using FIG. 2. FIG. 2 shows the conditions of main scanning and sub-scanning of the manuscript 1 indicated in FIG. 1. In this figure, the main scanning is carried out in the direction indicated by the arrow A and the image sensor reads picture data of the lines in this direction. The lines L.sub.1, L.sub.2, L.sub.3, . . . are read in this sequence. The arrow B indicates the sub-scanning direction and each paper feed moves the paper in the length indicated by b. Therefore, the image sensor reads picture data in the area ab formed by the length a of main scanning and the width b as the picture data of respective lines.
In the abovementioned transmission method of picture signal, the transmission time for picture data of blank portion is curtailed and the send time can be also curtailed. For example, the picture data of the line L.sub.2 is read during the period of send processing for the picture data of line L.sub.1. Moreover, the manuscript 1 for reading picture data of the line L.sub.2 is moved simultaneously with start of send processing for the line L.sub.1.
This means that it is required for reading picture data of the line L.sub.2 to move the line L.sub.2 to the position of image sensor by the sub-scanning and to read picture data of the line L.sub.2 during the period T from start to end of send processing for line L.sub.1.
In such a case, the sum of times of sub-scanning for paper feed and read time of image sensor 6 may become longer than the period T. Thereby, data read by image sensor 6 is started simultaneously with the sub-scanning. In this supposition, the picture data of line L.sub.3 is read during the period of sending picture data of line L.sub.2 as the abovementioned read condition. In this case, the sending process period becomes shortest since the line L.sub.2 is all white. Therefore, data read by image sensor 6 is started simultaneously with the sub-scanning. At this time, the image sensor 6 reads picture data of the line L.sub.3 including the black picture data l.
However, since data read is carried out during sub-scanning, the read area becomes wider than the area ab and may become 2ab (line L.sub.2 and line L.sub.3) in the worst case. In such a case, picture data of black indicated by l in the line L.sub.3 causes a discrimination error to occur because a difference in amount of charges corresponding to the picture data of black and white among those to be stored in the image sensor 6 becomes small since such picture data occupies relative a smaller rate in the data read area, and resultingly picture data of black l in FIG. 2 cannot be transmitted.
This is explained upon reference to FIG. 3. FIG. 3 indicates an output of the image sensor 6. In the case of ordinary output,
As shown in FIG. 3(a), there is a sufficient signal level difference between the picture data of white W.sub.1 and the picture data of black B.sub.1 in the ordinary output and resultingly the signal is accurately discriminated into the white signal W and black signal B by the threshold level TH.
But as in the case of reading the picture data of the line l indicated in FIG. 2 as explained above, a signal level difference between the picture data of black B.sub.1 ' and picture data of white W.sub.1 ' becomes small as indicated in FIG. 3(b) and it can no longer be read by the threshold level TH. In this case, picture quality to be transmitted is deteriorated. Existingly, following measures have been taken in order to prevent deterioration of picture quality resulting from such cause.
(1) The read time of image sensor 6 is curtailed by irradiating a manuscript with a large amount of light. PA0 (2) A manuscript is fed by driving mechanism with a motor having a large torque in view of realizing high speed feed of manuscript. Thereby the moving rate of manuscript is curtailed and picture data is read while the manuscript is in the stationary condition.
However, in the case of (1), it is required to used a specially designed lighting device in order to irradiate a manuscript with a large amount of light and also to use a specially designed power supply which is independent of that of the facsimile equipment, thus resulting in such disadvantage that the system becomes large in size and uneconomical. Moreover, in the case of (2), driving by a motor is always accompanied by noise and an economical disadvantage. It is also inferior to the facsimile system.